Radio receiving system



Sept. 16, 1941.- R. A. wl-:AGANT 2,256,070

RADIO RECEIVING SYSTEM Filed July 9, -1940 2. sheets-sheet 1 /PEGENERAr/VE AMPL/F/ER IN VEN TOR x ROY A. WEAGANT JW-I.. BY #5g /ao-u-OL/ Y ATTORNEY I R. A. WEAGANT 2,256,070

RADIO RECEIVING SYSTEM Filed July 9, 1940 Sept.` 16, 1941.

2 Sheets-Sheet 2 INVEN TOR ROY A. WEAGNT BY w/ww T ATTORNEY Patented Sept. 16, 1941 2,256,070 IiADIo RECEIVING SYSTEM Roy A. Weagant, Douglaston, Long Island, N. Y., assigner to Radio Corporation of. America, a

corporation of Delaware Application July 9, 1940, serial No. 344,488

11 claims. (c1. 25o-20) My present invention relates to radio receiving systems, and more particularly to systems of the type using carrier exaltation networks in connection with phase detection.

In prior applications I have disclosed and claimed various networks constructed and arranged to detect the signal energy of a desired carrier frequency even though strong adjacent channel interference existed, or even though strong static disturbance impulses were being collected. Essentially, these earlier disclosed systems comprised phase detection circuits wherein the desired signal energy was impressed upon a detector network with highly amplied oscillations of substantially the signal carrier frequency.

One of the main objects of my present invention is to provide an improved type of receiving system which utilizes phase detection networks, and wherein there is utilized phase detection stages in cascade thereby greatly to improve the selectivity of the receiving system, as Well as to increase the rejection of static disturbances.

Another important object of this invention is to provide a receiving system which utilizes a prior network constructed and'arranged to derive from modulated signal carrier energy second harmonic ener-gy, and a subsequent detection stage being employed to combine the modulated second harmonic energy with highly amplified second harmonicy energy whose modulation frequency components have been substantially all removed.

Another object of this invention is to arrange in cascade a plurality of signal transmission stages, and in each of the stages combining the signal energy with highly amplified unmodulated voltage of a frequency which is substantially equal to the mid-band frequency of the signal energy applied to each of said stages.

Still another object of the invention is to improve greatly the selectivity of a receiving system, as well as greatly to reduce the effect of static disturbances on the latter, by converting received signal energy to an intermediate frequency, then combining the 'intermediate frequency energy with highly amplified voltage of the intermediate frequency carrier substantially free of modulation components thereby to produce signal energy of th'J second harmonic of the intermediate frequency carrier, and finally combining the second harmonic energy with unmodulated voltage of substantially the second harmonic frequency in a detection network.

And still other objects of theinvention are to improve generally the efficiency and selectivity of radio receiving systems, and to provide such systems in a reliable manner capable of economic construction and assembly.

The novel features which I believe to be characteristic of my invention are set forth in par- .ticularity in the appended claims; the invention itself, however,. as to both its organization and method of operation will best be understood by reference to the -following 'description taken in connection with the drawings in which I have indicated diagrammatically several circuit organizations wherebyr my invention may be carried into effect.

y In the drawings:

Fig. l shows a receiving system which embodies `the invention,

Fig. 2 illustrates a modification,

Fig. 3 shows still another modification.

Referring to Fig. 1, there is shown a superheterodyne type of receiver which may be of the ytype utilized in the standard broadcast receiving range `of 550-1'700 klocycles (kc.). It is to be understood, however, that the invention is not restricted to this receiving range, but may be used with equal utility in the other well known frequency bands of radio communication. The signal Icollector device l is shown as of the grounded rantenna type, but it may be a loop co1- lector or radio frequency distribution line or even thev type of signal collector device used on a mobile vehicle, such as an automobile. The collected signals are preferably directly impressed upon the tunable input circuit 2 of a converter netWorkB. The converter Vmay be of the combined local oscillator-rst detector type using a pentagrid tube, but it may also embody independent local oscillator and first detector tubes, if desired. The numeral 4 denotes a tunable oscillator tank circuit, and each of circuits 2 and 4 includes independent tuning devices such as variable condensers. The dotted line 5 designates the mechanical uni-control arranged to adjust the rotors of the variable tuning condensers of circuits Zand 4. Of course, circuit 4 willbe tuned over a local oscillation fref quency range which is higher than that of the signal frequency range by the operating intermediate frequency (I. F.) value, and the I; F. value may be chosen froml a range of 75 to 456 kc.

The resonant output circuit 6 of the converter is tuned to the I. F. value, and is coupled to the tunedz input circuit 'l of the I. F. amplier tube 8. The latter may be of the 6L7 type. This type of tube has five grids arranged between its cathode 9 and plate I 0, and the first grid'll may be connected to one side ofthe input circuit 1.' The j Y tial end of coil I9.

is connected to a source of Vpositive potential,

of positive V.potential Yis shunted by tuning rcondenser'21l.

mid-'point of the coil of circuit I is established at ground potential with'respect to alternating 4currents, and a direct current blockingY condenser The third grid` I3..is.surrounded by a. positive screening field, and the grid itself` is connected Y to a source of highly ampliied voltage of I.` F.

v value.

This source of voltage is a regenerative amplier comprising tube I4 which has its output .closed in myco-pending'application Serial No.

335,892 filed May 18, 1940.

designated by the numeral 29. Resistor 29 is connected between the anode 29 of diode and electrode I5 regeneratively coupled through .condenser I to the control grid Il. Thegrid Il is.

connected to the lower end Yof* ,mputcircuitl While the grid I3 is connected through a vdirect current blocking condenser I8 to the high poten- The opposite -end of -coil I 9 while condenser 2li arranged inshunt with`coil I9 resonates the coil (to Athe I. F. value. 'The grid leak vresistor 2l connectsgrid' ISLtc :ground thereby establishing the gridxil .at .'adirectcurrent voltage which is .negative'withrespect to .cathode 9by the 'voltagefdrop acrlss resistor l2.

The cathode 'of tube` Ill fis .connected to :ground through the .self-'biasing' resistor 22 'which is shunted by the yusual 1I. bypass condenser.

The function Yof tube VM', and its'f associatedxcircuits; is lto feed togrid 'I3 voltage :of the-I. F.

- value which iis substantially freejof .all modulation frequency components. That is.the regenerative amplifier tube I4 functions to exalt, or

stantially strips away all modulation components Y up to about twoor .three'ihundred-.cyclesfjiOf course, .even .the 4 latter. components may 'be removed. Y

The plate Ii of tube 8 is connected to'asource work 24"-23 -is tuned to .the second 'harmonicof the I. F. carrier value. Hence, if :the I Fxva'lue I is 450 kc.,- by wayv of illustration, .then circuit 2li-23 is tuned to '900 kc'. 'It will loe noted that there is 4impressed on the .grids yII @land I3 of tube' voltages of .the I.- F. carrierfvalue; The tube `8 functions in the manner .of'a'mixer tube', and the voltages on grid I'I .and 'I3 are applied inrfopposite phase. Hence, -`'the rectified output voltage Vappearing across :output circuit'224-23 will be proportional to .the product of `the accentuated, or exalted, I. F. carrier voltagefdellivered by tube II4 'andthe I. F. signal`input delivered to grid AII. There are developedrin Ythe output circuit V2li-23 of mixertube i8 `two products of rectication. These are laudio .frequencies and the second harmonic of the signal input vfrequencies. f

.The audio kfrequencies `are V.excluded-by vvirtue of the` a'ct that the .output circuit istuned Ato the second harmonic ofjthe'I.V F. carrier value. When modulationfexists on fthe' desired .I signal Y carrier there 'will exist` `in Ythef output circuit 24-23 ltheusual modulation side .bands of double frequency. It `is highly desirable .that the Ymixer tube '-8 have --agsquare layv rectification characteristic foreweakgsignals; and that Athe signalrvol'tage of grid .Il beV Very small-inproportion to the 'accentuatedL F. carrier voltage fed tovgrid I3. v.Attention 'is directed to the phenomenon of. selective improvement 1in detector efficiency which occurs in suchqa case, as ydis-N The net-1 i5Vv lcirc 't 28 s vconnected to ground through a through the Acoupling Y regenerative -cjuencyY currents.

nected to ground through VThis second regenerative order to Vby-pass all high irewith resistor 29 in The low potential side of input resonant circuit 3I which is tuned to the second harmonic of the I. F. There is injected into circuit `3| the highly amplied unmodulated voltage whose frequency is equal to the second harmonic of theI. F. This is accomplished by con- -necting the plate of vtube 32 to its signal grid condenser 33, and impressing upon the grid of tube 32 the second harmonic signal Venergy developed across circuit 2lb-23. r

The-condenser 34 'connects the grid of tube 32 to the plate 'I0 of mixer tube 28. vIn the-plate circuit Ioftube 32 there is included a resonant circuit 35 which is .tuned yto the second harmonic of the I. F., circuit 35 being magnetically coupled to `vcircuit 3l so as to provide .a sharply selective circuit. The cathode of tube '32 is :con-

a'properly by-passed bias resistor 36.' The tube circuits provide Va second regenerative amplifier which is similar in construction to the regenerative amplification circuit Vembodying tube I4.

amplier circuit functions Vto provide accentuated unmodulated voltage lof a frequency equal to the second har- Vmonic of the I. F.

Due to the relatively high selectivity of the connection and the selective network 35-3I, the voltage developed across ci-rcuit 3I is relatively reeof modulation components, and, therefore, is substantially'voltage of .double the I. F. carrier. This voltageis appliedto Vthe diode 26 along with the signal v.voltage Yappearing across circuit 23, and vthetvvo voltages are .in the same or opposite phase. Here, again, it is required that the accentuated unmodulated second harmonic voltage be of relatively Vhigh magnitude withA respect to the signal voltage developed across circuit 28. There is rsecured a selective improvement in detector efliciency .in this second detector stage Vas disclosed in my aforesaid co-pending application.

Detection takes place, and there is developed across resistor 29 audio voltage components'as well as direct current voltage components. The audio frequency voltage is taken off by a slidable ltap 36, .and is then fed to one or more audio .frequency amplifiers which may be iollowed .by any desired type oi reproducer.

The direct current voltage components'are utilized .ierautcmatic volume control (AVC) r action.V This is accomplished by connecting theV signal grids of regenerative amplier tubes I4 terminate in an adjustable tap 38 so as to providev anr adjustment -of gain control bias. Proper filter resistors 39 may be included in the AVC line so `as to prevent pulsating voltage components .from being applied to the grids of tubes The cathode of diode 26 is con- 32 and its :associated The lead 31 may Y I4 and. 32. The AVC connection functions to control the regenerative amplifier tubes in` a sense such as to maintain signal voltage across circuit 28 substantially uniform regardless of signal carrier amplitude variation at collector I over a wide range. The AVC arrangement, ad-

ditionally, functions to reduce the gain ofthe regenerative amplifier tubes simultaneously with the reduction of the gain of tube 8 as the carrier amplitude increases. In this way there is maintained a fairly proportional relation be tween the signal voltage applied to each of the mixer and detector tubes and the accentuated carrier voltage.

It will now be seen that there has been provided at least two networks in cascade, each' of which utilizes selective improvement in detector efficiency. The rst of the stages functions to produce signal voltage of double the I. F. value, whereas the subsequent stage derives from the second harmonic signal voltage the desired modulation component voltage. There is thus secured an improvement in the over-all selectivity which is analagous to the increase in amplification obtained by two stages.

In Fig. 2 there is shown a modification of the system wherein there is employed two pair of push-pull, or balanced, mixer tubes in cascade. In other words, in place of the signal tube 8 employed in the I. F. mixer stage, there is utilized a pair of tubes 40 and 4| each of which may be of the same type as tube 8. The cathodes of the tubes 40 and 4| are connected in common to a properly by-passed grid bias resistor 42, while the plates of the two tubes are connected to the opposite sides of the second harmonic output circuit 2li- 23. The mid-point of coil 23 may be connected to a source of positive potential. The signal grids of tubes 40 and 4| are connected to the opposite sides of input circuit 1, while the third grids 43 and 44 of tubes 40 and 4| respectively are connected to the output circuit 45 of the regenerative amplifier tube I4. It will be noted that an additional tuned stage is interposed between grids 43, 44 and the plate circuit 2li- I 9 of tube I4 in order to secure correct phase relation between the exalted carrier and the signais. Furthermore, the grid I1 of tube I4 is coupled to the primary circuit 6 by condenser 4B. Otherwise, the regenerative amplifier stage is similar to that shown in Fig. l associated with tube 8. Here, again, the regenerative amplier functions to accentuate the I. F. carrier while substantially removing all of the modulation voltage components Hence, there is applied to grids 43 and 44 Voltage of the I. F. value which has practically no modulation components. However, to the signal grids of tubes 40 and 4| there is applied in push-pull relation the normal I. F. signal voltage. In each of tubes 40 and 4| the voltages on the respective grids 43 and 44 are in like and unlike phases with the I. F. signal voltage on each of the signal grids.

There is developed in the output circuit 24-23, as in the case of Fig. l, Voltage of double the I. F. value. The detector input circuit 28Vr has the mid-point of its coil connected to ground, and

the signal grids of the detector tubes 50 and 5|v are connected to opposite sides of input circuit 28. The common cathode lead of the two tubes is connected to ground through a properly bypassed bias resistor 52. The input circuit 28 is, also, tuned to the second harmonic of the I. F. value. The plates of tubes 50 and 5| are connected in push-pull relation. That is to say, they are connected to the opposite ends of the primary Winding of audio transformer 53, and the mid-point of the primary winding is connected to a source of positive potential. Tubes 50 and 5| are otherwise arranged in a manner similar to the arrangement of tubes 40 and 4|. In other words, the third grids of each of tubes 50 and 5| are connected to the output of a second regenerative ampliiier stage. f

The second regenerative amplifier stage comprises, as in the case of Fig` 1, the tube 32. The coupling condenser 34 connects the grid of tube 32 to the plate of tube 4|. Hence, there is applied to the tube 32 signal voltage of the second harmonic of the I. F. Both the selective circuits 35 and 3| are tuned to the second harmonic frequency as in Fig. 1. As explained in the latter case, the regenerative amplifier strips the modulation component frequencies from the second harmonic carrier, and across circuit 3| there is developed voltage of substantially the I. F. second harmonic. This voltage is applied to the grids 60 and 6| of tubes 50 and 5| respectively. The voltages applied to grids 60 and 8| are in like and unlike phase with the signal voltages applied to the respective signal grids of the tubes. The accentuated double I. F. voltage is relatively high in magnitude with respect to the signal voltages applied to the signal grids. The tubes 50 and 5| act as a balanced detector, and audio `modulation component voltage appears across the output transformer secondary winding.

The gain control is provided in this case by a separate diode 10, whose anode 1I is coupled to the high potential side of circuit 3| by coupling condenser 12. The load resistor 13 is connected betweenthe anode 1| and the grounded diode cathode. The AVC connection is made from the load resistor 13 to the grids of each of the tubes I4 and 32, nlter resistors 39 beingemployed to suppress pulsation voltage components. Slider 14 may be adjusted along resistor 13 to select a desired bias value.

In the modification of Fig. 3, the balanced tubes 50 and 5| are replaced by a pair of balanced diodes. The latter may be housed in a common tube 88, such as one of the 6H6 type. Thus, anode 8| is connected through condenser 82 to one side of input circuit 28, while anode 83 is coupled through condenser 84 to the opposite side of circuit 28. 'Ihe accentuated second harmonic I. F, voltage is injected into the detector network by connecting the high potential side of circuit 3| to the mid-point ofthe coil of input circuit 28. The AVC connection 31 is made to the mid-tap on load resistor 9D connected between anodes 8| and 83.

The cathodes of the diodes are connected to the grounded mid-tap of resistor 9|. The second harmonic by-pass condenser 92 shunts one half of resistor 9|, while by-pass condenser 93 shunts the other half. The audio voltages at the opposite ends of resistor 9| are applied in push-pull relation to the signal grids of the twin-triode tube |68. The audio output transformer IUI. having its primary winding in push-pull connectionwith the plates of tube |08, feeds the audio voltage to following stages. There is had full wave rectification of the applied fully modulated second harmonic voltage and accentuated second harmonic voltage. The rectification in each half of the network is similar in action to that had with the network in Fig. 1. Resistor 30 supplies. the Al/C; bias,5 and also. acts as a, 5115er resistance,I Y

While I- have indicated and` described several systemsv for carrying my invention into'y effect, it will, be appa-rent to. one skilled. in `the art that my invention is by no means limited to the particular ,organizations shown and described, butfthat many modifications may be made Withoutrdeparting from the scope of my invention, asset forth in the appendedV claims.

What I claim is;

Y1,111 a system for receiving modulated carrier energy, lthe method which includes reducing the energytoa lowerY carrier frequency, producing unmodulated energy of'said reduced carrier fre- V quency., heterodyning the modulated vcarrier energy ofV reduced frequency with said unmodulatedenergy ofk said. reduced carrier frequency, deriving from the combined energies modulated carrier energy of an harmonic of said reduced frequencyproducing unmodulated: energy of said harmonic frequency,l combining said modulated harmonic energy withsaid unmodulated energy Vof said harmonic frequency to produce energy Vsaid harmonic frequency, andrectifying the last named Vcombined energies thereby to produce enengyA ofthe modulation component frequencies. 3. In a system for receiving modulated carrier Y energy, the'k method which includes reducing the.

energyv to a lower carrier frequency, producing unmodulated energy of said reduced carrier fre- 4 quency, l'ieterodyni'ng' the modulatedV carrier energy of rreduced frequency lwith said unmodulated energy of saidv reduced's'carrier frequency, deriving from the combined energies modulated carrierI energy of an harmonic .of Asaid reduced frequency which is doublesaid carrier frequency, removing substantially all-the modulation from a portionrof said modulateddouble harmonic en-l ergy thereby-toprovide unmodulated double harmoniccarrier energy, 'combining said modulated harmonic energy vvithl said unmodulated energy of said double harmonic frequency to produce energy of the modulation component frequencies.

4. In a system for receiving kmodulated carrier energy the method which includes reducing the energy to a lower carrier frequency, stripping the modulation from-- a portion of the modulated reduced Ycarrier energyto provide unmodulated reduced carrier energy, heterodyning the'modulated vcarrier energyA of reduced frequency with said unmodulated' energy of said reduced frequency, deriving from the combined energies modulated carrier energy of an harmonic of said reduced frequency,` producingV unmodul'ated `energy of said harmonic frequency, combining said harmonic energy with, said unmodulated energy of saidY harmonic frequency to produce energy of the modulation component frequencies, and varying the magnitudes of saidunmodul'ated enertenero gies in; responscltqamplitude variations in said Y carrier'. energy. Y Y

54111 ani audio-modulated; carriervoltage, rc.- cei'ving' system Ythe4 methodA .which includes, con.- vertirig ccllectedfcarrier ,voltager toY modulated carrier volt'ags:V of'. intermediate, frequency, de-

riving substantiallyunmedulatedcarrier voltage of. said intermediate vfrjequen'cy frmQSadmQdu.- lated intermediate frequency voltages, QQmbining said modulated.intermediatey frequency voltage. with saidl substantiallyunmodulated voltage, of said intermediate frequency; ,deriving from the combined voltages modulated carrier v0 ltag v of a frequency which is a'multiple'of saidintermediate, frequency, deriving from'said modulated Amultiple frequency every substantiallyiunmodulated voltage, of vsaid multiple frequency, combining said modulated multiple frequency carrier voltage Withsaid substantially unmodulated'voltage of saidmultiple frequency thereby to produce voltage of audio frequencies.

6'. In an -audio-modulated carrier voltage receiving system, the method which includes converting collected carrier voltage'to modulated carrier voltage'of intermediate frequency, producing substantially unmodulated voltage of intermediate frequency, combining said modulated intermediate frequency voltage with said substantially unmodulated voltage of said intermediate frequency, deriving from the combined voltages modulatedl carrier voltage of a frequency which is a second' multiple of said intermediate frequency, producing substantially unmodulated voltage of said multiple frequency, combining said modulated multiple frequency carrier voltage vvithv substantially unmodulated voltage of said multiple frequency thereby to produce voltage of audio frequencies and varying the magnitude of' said unmodulated voltages in accordance with variations in the amplitude of said carrier.

7. In armodulated carrier energy receiver'system, producing unmodulated energy of a predetermined carrier frequency, mixing modulated carrier energy of-'said predetermined carrier frequency with said unmodulated carrier energy of the same frequency thereby to produce modulated carrier energy of at least double said carrier frequency, removing from a portion of said modulated double carrier Vfrequency energy Vsubstantially all modulation, mixing said double' fre-V quency modulated energy with said unmodulated carrier energy of said double frequency, and deriving from the lastl mixed' energies voltage of the modulation component frequencies.

8. In a modulated carrier energy receiver sysi tem, producing unmodulated energy of a predetermined carrierfrequency, mixing modulated carrier energy of said predetermined carrier frequency. Withsaid unmodulated carrier energy of the same frequency in phase opposition thereby to produce modulated carrier energy ofv at least doubley said carrier frequency, removing from a portion of saidy modulated double carrier fre? quency energy substantially all modulation, mixing said double Vfrequency modulated energy with said' unmodulated carrier energy of said doubleY frequency in phase opposition, and deriving from the last mixed energies voltageV of the modulation frequency, means mixing Vsaid latter modulated energy with said unmodulated energy in phase opposition to produce modulated carrier energy of the second harmonic of said reduced frequency, means deriving substantially unmodulated carrier energy of said second harmonic frequency from said second harmonic modulated energy, and means for rectifying combined second harmonic modulated and unmodulated energies to produce voltage of modulation component frequencies.

1G.In a modulated carrier energy receiver, means for reducing said energy to a lower carrier frequency, means deriving substantially unmodulated carrier energy of said reduced frequency from said modulated energy of reduced frequency, means mixing said latter modulated energy with said unmodulated energy in phase opposition to produce modulated carrier energy of the second harmonic of said reduced frequency, means deriving substantially unmodulated carrler energy of said second harmonic frequency from said second harmonic modulated energy,

and full Wave rectification means'for rectifying combined second harmonic modulated and unmodulated energies to produce voltage of modulation component frequencies.

ll. In a modulated carrier energy receiver, means for reducing said energy to a lower carrier frequency, means deriving substantially unmodulated carrier energy of said reduced frequency from said modulated energy of reduced frequency, means mixing said latter modulated energy with said unmodulated energy in phase opposition to produce modulated carrier energy of the second harmonic of said reduced frequency, means deriving substantially unmodulated carrier energy of said second harmonic frequency from said second harmonic modulated energy, and means for rectifying combined second harmonic modulated and unmodulated energies in phase opposition to produce voltage of modulation component frequencies.

ROY A. WEAGANT. 

